Hello I have build up an Storage system with zfs on Openmedivault base
the proformance an stability is ok but now I'm not sure about my configuration I'm not sure above my raid configuration.
And after an Loss of one of my Hardisk I'am able to replace them but I'am not sure
when i look at the Status what is configured really and and what exactly could be broken if a different disk is broken .
The ideas was to create 3 unindependend mirror of disk which then will be mirrored again
like an Raid 10 in an normal array but I'am no longer sure that i have this now
can anyone help me to get a clear picture .
I 'also configure two SSD Disk break them into two Partition and mirror them again each other and use one partition as an ZIL and the second Partition as an ARC Cache for performance also this I want to diskuss it this is a good idea or not .
Thanks in advance for every answer also on that .

here are the Output of my POOL Status
root@FWOMV:~# zpool status
pool: DATA
state: ONLINE
status: Some supported features are not enabled on the pool. The pool can
still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
the pool may no longer be accessible by software that does not support
the features. See zpool-features(5) for details.
scan: scrub repaired 0 in 3h6m with 0 errors on Sun Dec 20 06:06:58 2015
config:

Your OCZ SSDs are NOT suitable for use as sLOG device. Your current configuration basically means you have the ZIL disabled - which is not recommended. If you remove the sLOG devices from your pool configuration, you will still have a ZIL since it will be stored on the harddrives themselves.

You can safely use OCZ SSDs as Cache though - caching is always safe. If corruption occurs, the data will be read from your HDDs instead thanks to ZFS' checksumming feature.

Your pool configuration is a bit weird though. You basically have a RAID0 of a 2-disk mirror and a 4-disk RAID5 or RAID-Z. This is not a common configuration and the loss of two disks will likely render your pool inaccessible. Better would be a configuration of a single RAID-Z2 of 6 disks. So the same number of disks, the same overhead, but still better protection.

You cannot change this without losing data though. Meaning, you need to destroy your current pool and re-create it.

If you have no means to transfer the data to a temporary location, you might try this trick: remove one disk from the mirror vdev and one disk from the RAID-Z vdev. Then you have two disks on which you can create a temporary pool. Then transfer the contents of your current pool to the temporary pool if that fits on two disks. Then destroy your current pool ('DATA') and re-create it using a single RAID-Z2 pool consisting of 6 disks, with just 4 disks being present. This is possible by using two memory disks. After having created it, reboot to remove the memory disks. Then you have a double degraded pool and your temporary pool. Then transfer from the temporary pool to the new pool and after that you can remove the temporary pool and add the two disks to the new array, making it complete again.

Just an idea. RAID-Z2 offers good protection by being able to lose two disks without losing the entire pool.